There have been developed innumerable different toy building blocks, beams, panels and the like with joinder means of varying complexity for children to simulate building all types of constructed units. Reference is made, for example, to U.S. Pat. Nos. 1,000,395, 2,156,155 and 3,581,431. Such toys are generally intended for "table top" use to form small scale replicas of adult bridges, towers, buildings and the like and many incorporate some type of snap-on connection or interlocking parts for joinder of elements. The famous "Erector Set" of the thirties employed bolts and nuts to join perforated beams to form a myriad of different structures.
The present invention provides a lightweight building block system that may be employed by children to build enclosures large enough for entry by the child and yet strong enough to withstand being played with and on by children.